1. Field of the Invention
The present invention relates to the field of printers designed to produce a hard copy printout when operated on line or in association with a digital data system wherein the printer includes a self-diagnostic control means to accept the digital data, synchronize the production of the corresponding hard copy printout, provide programmed paper feed, and to perform internal, self-diagnostic functions to monitor, analyze and communicate status changes and fault conditions.
2. Description of the Prior Art
Prior art printers, designed to produce hard copy in cooperation with digital data systems, have previously used MSI ROM controlled logic to perform housekeeping functions regarding the acceptance and transference of data from the digital data system to the hard copy printer. In such prior art ROM controlled printers, diagnosis and analysis schemes have been rudimentary and communication of the status or fault to the user, system or operator has been limited and nonspecific. Typically, the control logic of the printer is circuitry which is capable of operating in a distinct number of phases or modes to perform the minimal number of data acceptance and transfer functions. For example, a load mode to receive and store print characters and paper motion characters; a justification mode to left justify data and line buffers; an illegality mode to check for the presence of illegal characters; a print mode to print the contents of line buffers; and a format mode to start execution of the paper motion character. Thus, the logic was highly specialized and limited to the necessary functions to transform digital data into hard copy printout. A typical prior art dedicated logic printer system is disclosed in the U.S. Pat. No. 3,651,487 to Washington. If an option is to be added, logic redesign is typically required. Furthermore, the logic circuitry designed to check for error analysis and status diagnosis is similarly specialized to the required and necessary tasks at hand. Therefore, status and fault diagnosis is limited by the architecture and capability of diagnostic circuitry. As a result, the number of diagnostic functions and the ability of the printer to analyze, isolate and communicate a particular status or fault condition is limited to merely the necessary functions. Each of these disadvantages have been overcome by the present invention without entailing greater costs or increasing circuit complexity.